Supporting actors, the French king moves (7)
I believe the answer is:
castles
'king moves' is the definition.
'castles' can be an answer for 'moves' (castle is a kind of move). I'm not sure about the 'king' bit.
'supporting actors the french' is the wordplay.
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go under others).
'actors' becomes 'cast' (I've seen this before).
'the french' becomes 'les' (les is the in french).
'cast'+'les' is 'CASTLES'.
Can you help me to learn more?
(Other definitions for castles that I've seen before include "Men" , "big houses" , "Large and stately mansions" , "Rooks" , "Don't build the chess pieces in the air" .)